The present disclosure relates to a controller and a control method for an internal combustion engine mounted on a vehicle.
For example, Japanese Laid-Open Patent Publication No. 2004-218541 discloses a controller that executes dither control. In the dither control, when there is a requirement for an increase in the temperature of a catalyst device (exhaust purification device), at least one of the cylinders is treated as a rich combustion cylinder, in which the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and the remaining cylinders are treated as lean combustion cylinders, in which an air-fuel ratio is leaner than the stoichiometric air-fuel ratio.
When executing the dither control as described above, the torque generated by the combustion in the lean combustion cylinders is smaller than the torque generated by the combustion in the rich combustion cylinder. This increases the rotational fluctuation of the engine crankshaft. For this reason, the execution of the dither control when the user is likely to feel the vibration of the internal combustion engine as during idle time may cause the user to experience discomfort.